/* FILE: isPrime-v2.cpp
   tests n potential primes entered by user, using an EOF-controlled loop
   employs user-defined function, isPrime()
 */

#include <iostream>
using namespace std;

//prototypes
bool  isPrime(unsigned long n);

int main(){
  int n,          //input integer
    pd;         //potential divisor

  //prompt and read n
  cout << "enter n > 1 (c-d to exit): ";
  cin >> n;

  //driver loop
  while(cin){
    //display result
    cout << endl <<  n
	 <<  ((isPrime(n)) ? " is prime " : " is composite" );
    
    //prompt and read n
    cout << endl <<  "enter n (c-d to exit): ";
    cin >> n;
  }
  
  //quit
  cout << endl << "Exiting..." << endl;

}


/* isPrime()------------------------------------------------------------------
 * simple, brute-force predicate for prime numbers
 * returns true if n is prime; otherwise returns false
 */
bool isPrime(unsigned long n){
   unsigned long pd = 2;                //potential divisor

   //generate and test divisors
   while(n % pd != 0)
      pd++;

   //return result
   return (n == pd);
}